Field of the Invention
The present invention relates to wireless communication, and more particularly, to a cell searching method performed by a terminal in a wireless communication system, and the terminal using the method.
Related Art
In an International Telecommunication Union Radio communication sector (ITU-R), a standardization of International Mobile Telecommunication (IMT)-Advanced being a next mobile communication system after a third generation has been performed. The IMT-Advanced is aimed at supporting an Internet Protocol (IP) based multi-media service with a data transmission rate of 1 Gbps in a stop and low speed moving state and a data transmission rate of 1 Gbps in a high speed moving state.
A 3rd Generation Partnership Project (3GPP) is preparing LTE-Advanced (LTE-A) being an improved one of Long Term Evolution (LTE) based on an OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission scheme as a system standard satisfying requirements of IMT-Advanced. The LTE-A is one important candidate for IMT-Advanced.
In recent years, there is growing interest in a Device-to-Device (D2D) technology performing direct communication between devices. In particular, the D2D is attracting attention as a communication technology for a public safety network. A commercial communication network has been rapidly changed to the LTE but a current public safety network is based on a 2G technology in a collision problem and a cost side with an existing communication standard. Request for the technology clearance and an improved service induces an effort to improve the public safety network.
The public safety network has high service requirements (reliability and security) as compared with a commercial communication network. In particular, when coverage of cellular communication is insufficient or is not used, there is a need for direct signal transmission/reception between devices, that is, a D2D operation.
The D2D operation may be signal transmission/reception between adjacent devices to have various advantages. For example, a D2D terminal may perform data communication with a high transmission rate and low delay. Further, the D2D operation may distribute traffic converged in a base station. If the D2D terminal serves as a relay, the D2D terminal may serve to extend coverage of a base station.
Meanwhile, the D2D operation may be performed not only inside the coverage of the base station (i.e., cell coverage) but also outside the coverage of the base station. When located outside the cell coverage, a terminal may perform the D2D operation by using a predetermined resource since it is difficult to allow a resource to be scheduled by the base station. A preconfigured resource for the D2D operation may be given in a specific frequency band.
However, if the terminal performs the D2D operation, in particular, D2D signal transmission, in the specific frequency band, this may cause an interference to cellular communication. That is, if a frequency used for the D2D operation is the same as or different from a frequency used in cellular communication, D2D signal transmission of the terminal may act as an interference to cellular communication of the base station or another terminal. Accordingly, there is a need for a method for minimizing the interference caused by the D2D operation of the terminal on the cellular communication.